A veteran journalist and documentary film maker, known for asking difficult questions of climate scientists and politicians, has been denied press accreditation for the Cancun Climate conference.

The UN has refused access to the Cancun Climate Conference to Phelim McAleer, who is well known for asking scientists and politicians difficult questions about Global Warming orthodoxy.

McAleer was notified of the UN's refusal to accredit him just days before the international conference, which opens today.

McAleer produced and directed Not Evil Just Wrong, a documentary on Global Warming, and his reports from Copenhagen Climate Conference went viral on Youtube.

During one encounter an armed UN security guard prevented McAleer from asking a scientist difficult questions about the climategate questions and warned that if he did not stop filming he would confiscate their equipment and expel him from the conference.

McAleer says the refusal to allow him access to the Cancun Climate conference is censorship.

"I sent them exactly the same documentation that was acceptable for Copenhagen one year previously, but it seems they did not like my coverage of Copenhagen and are now trying to silence me and the people who have questions about this process," said McAleer.

"The message is clear—ask UN scientists and politicians difficult questions and you will be banned from any UN sponsored events. No difficult questions allowed," he added.